The present invention relates to a fluid treatment and distribution system and, more particularly, to an apparatus and method for the aeration of a liquid such as waste water effluent or sewage.
Aeration of fluids achieves peak efficiency when thorough mixing and circulation of the parent fluid results in the entrainment of air within the liquid in the form of small bubbles and the suspension of the contained solids. Known types of aeration devices include propeller mixer equipment, paddle wheel arrangements and fountain systems. The use of any mechanical aerator increases the rate of oxygen uptake per unit time, as compared to an unaerated body, by altering the mass transfer or contacting coefficient. A direct drive high speed surface aerator achieves this increased contact in a two-fold fashion: by breaking up the volume of water pumped directly through its discharge port into a spray of discrete particle sizes causing maximum air contact over the trajectory of the spray, and by mixing the parent body of fluid. The mixing effectively distributes the oxygen dissolved in the spray, creates surface turbulence and assures the maintenance of the greatest possible driving force to the process by keeping concentration uniformity throughout the volume of water, thereby avoiding saturation of the air-water interface. This surface air-water interface is constantly disrupted by the impingement of the spray jet with the parent body of water.
For most efficient aeration and circulation, it is desirable to draw the sewage liquid from that area nearest the bottom of the pond or tank and propel that liquid upwardly where it may be aerated, as by being thrust into the air outwardly and upwardly by a direct drive surface aerator described above. Generally, such aerator apparatuses are floating devices utilizing a top mounted motor. The power consumption necessary to draw the waste liquid into the intake channel of the aerator apparatus depends largely on the length of the intake channel at a given impeller speed. As a result, such aerators generally have an intake channel extending only a short distance into the body of the waste liquid. Such aerators cannot effect a complete fluid turnover of waste liquid from the lower depths to the surface, and therefore inefficient circulation results. Were the aerator apparatus set on the bottom of the pond or tank for drawing water from such lower depths, too much power consumption would be necessary to drive the water with sufficient force to lift it upwardly and outwardly from the surface of the water for sufficient aeration. To overcome such a problem it has been suggested that the contact time of the water with the air be increased in the mixing chamber (U.S. Pat. No. 4,030,859); or that water be drawn from the bottom of the pond, aerating the water through aspiration and then discharging the oxygenated water by a propeller into the pond in a downward direction (U.S. Pat. No. 4,086,306). In addition, various floating aeration devices have aspirated air into the incoming waste liquid prior to discharging it into the air, thereby increasing the contact of the liquid with the air for accelerating the solution of oxygen in the water (U.S. Pat. Nos. 3,365,178; 3,572,658; 3,846,516 and 3,512,864).
However, the introduction of air into the liquid by aspiration does not occur with any degree of force, nor does it generate any turbulence within the water. The amount of air introduced is not great, nor does it contribute to a significant degree to the actual mixing of the air with the water to promote aeration.